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Amount of time spent outdoors. A. Amount of time spent outdoors per day in weekdays in the surveyed Miami-Dade County population and the posterior gamma distribution. B. As A, but for weekends. C. As A, but data are taken from the NHPS survey on the U.S. population. Courtesy of Ajelli, et al (2017)
Whether a community is made up of people who spend their days entirely outside or those who rarely see sunshine, the amount of time residents spend outdoors can affect how Zika virus spreads throughout the population. That's the conclusion of a new study conducted in Miami-Dade County, Florida, and published this week in PLOS Neglected Tropical Diseases.
Zika virus--carried by Aedes mosquitos in select tropical and subtropical regions of the world--is often transmitted indoors in developing countries. But in the United States, the majority of mosquito bites occur outdoors. Therefore, local patterns of how people spend their time outdoors are likely to contribute to how mosquito-borne viruses, including Zika, are spread.
In the new work, Marco Ajelli, of Northeastern University, and colleagues at the University of Miami surveyed 270 residents of Miami-Dade County Florida about their time spent outdoors, and analyzed both the survey and previously published national data on outdoors time. Then, they used computational modeling to determine how Zika transmission dynamics related to time spent outdoors by people.
The researchers found that the amount of time spent outdoors by people in Miami-Dade County was highly variable; most people spent little time outdoors--less than two hours a day--but a small percentage of people spent a large amount of time outdoors. Their modeling then revealed that this heterogeneity--compared to a hypothetical population in which everyone spent the same, average amount of time outside--leads Zika virus to infect fewer people, but spread at a faster pace between people.
"This highlights the need to derive new indices to be considered by operational mosquito control programs, categorizing neighborhoods on the basis of both mosquito surveillance counts and human outdoor exposure risk," the researchers say. "Operation control efforts could be prioritized and directed toward areas characterized by high levels of human outdoor activities, such as recreational areas and tourist attractions, rather than, for instance, on residential areas."
Reference: Ajelli M, Moise IK, Hutchings TCSG, Brown SC, Kumar N, Johnson NF, et al. (2017) Host outdoor exposure variability affects the transmission and spread of Zika virus: Insights for epidemic control. PLoS Negl Trop Dis 11(9): e0005851.